Currently, multiple-input multiple-output (Multiple Input and Multiple Output, MIMO) technologies are widely applied to communications systems, such as a Long Term Evolution LTE) system. In the MIMO technologies, a transmit end and a receive end each use a plurality of transmit antennas and receive antennas, so that signals are sent and received by using the plurality of antennas of the transmit end and the receive end. The MIMO technologies can improve communication quality and a system channel capacity.
In a MIMO system, a precoding technology may be used to improve signal transmission quality and a signal transmission rate. A network device may estimate a precoding matrix for a downlink channel based on channel state information (CSI) fed back by a terminal device, and then the network device uses the precoding matrix to perform downlink transmission with the terminal device. For a high precision codebook-based precoding matrix defined in the LTE standard Release 14 (Rel-14) and a new radio access technology (NR), in a prior-art technical solution used by a terminal device to feed back CSI to a network device, the CSI fed back by the terminal device includes a rank indicator (RI), a precoding matrix indicator (PMI), and a channel quality indicator (CQI) of a channel matrix. The PMI includes a PMI1 and a PMI2, the PMI1 is used to indicate all elements in a matrix W1, the PMI2 is used to indicate all elements in a matrix W2, and a product of W1 and W2 forms a precoding matrix W. In this solution, since W2 is obtained based on a high precision codebook this solution has a problem of requiring a large quantity of bits and high resource overhead required for feeding back the PMI2 corresponding to W2.
As mentioned above, for the high precision codebook-based precoding matrix, the prior-art CSI feedback technical solution has a problem of high resource overhead required for CSI feedback.